1. Field of the Invention
The invention generally relates to a numerically controlled orbital machining apparatus for producing a hole in a workpiece by means of a cutting tool rotating about its own tool axis as well as eccentrically (orbiting) about a principal axis corresponding to the longitudinal center axis of the hole to be machined. More particularly, the invention relates to an improved mechanism of the apparatus for adjusting the radial offset (orbit radius) of the cutting tool axis relative to the principal axis.
2. Description of the Related Art
WO 99/62661 discloses an apparatus for machining a hole in a workpiece wherein the apparatus includes a spindle motor that rotates a cutting tool about its own center axis and wherein the cutting tool can rotate eccentrically about a principal axis corresponding to the longitudinal center axis of the hole. The apparatus includes a mechanism for adjusting the radial offset of the tool axis relative to the principal axis. Although the radial offset adjustment mechanism is configured such as to make it possible to change the radial offset during machining such that conical holes may be formed while simultaneously rotating the cutting tool about its own center axis and feeding the cutting tool axially into the workpiece, this mechanism is somewhat structurally complex and occupies a relatively large space in the longitudinal direction. The spindle motor is protruding substantially in a cantilevered manner from supporting structures of the apparatus, which may affect the precision of the machining results of the holes produced thereby.
It is an object of the invention to provide an improved and structurally simpler and a more compact radial offset adjustment mechanism of the present invention which is configured to allow a continuous radial offset adjustment of the cutting tool while simultaneously performing an orbital movement thereof about the principal axis and moving it in an axial feed direction into the workpiece, thereby making it possible to produce not only cylindrical holes or recesses but also holes or recesses having a conical or tapered configuration or sections thereof by using a substantially cylindrically shaped cutting tool.
For this purpose the apparatus of the present invention a first actuator configured for rotating the cutting tool about its longitudinal center axis during the machining of the hole;
a second actuator configured for moving the cutting tool in an axial feed direction substantially parallel to the tool axis, the second actuator being simultaneously operable with the first actuator;
a third actuator configured for rotating the cutting tool about a principal axis, the principal axis being substantially parallel to the center axis of the tool and coaxial with a longitudinal center axis of the hole to be machined, the third actuator being simultaneously operable with the first and second actuators; and
a radial offset mechanism configured for controlling the radial distance of the center axis of the cutting tool from the principal axis, wherein the radial offset mechanism includes: an inner cylindrical body having an eccentric cylindrical hole, the eccentric hole having a longitudinal center axis that is parallel to and radially offset from a longitudinal center axis of the inner body, the eccentric hole being configured to radially and rotatably support a spindle unit for operating the cutting tool; and
an outer cylindrical body having an eccentric cylindrical hole, the eccentric hole of the outer body having a longitudinal center axis that is parallel to and radially offset from a longitudinal center axis of the outer body a distance which is equal to the distance between the center axis of the eccentric hole of the inner body and the center axis of the inner cylindrical body, the inner cylindrical body being radially supported in the eccentric hole of the outer cylindrical body and rotatable therein so as to adjust the radial distance of the center axis of the cutting tool from the principal axis.
A further object of the invention is to provide a radial offset adjustment mechanism of the kind mentioned above, wherein the basic structural configuration of the radial offset adjustment mechanism is such as to allow for an accurate mass balancing of the centrically and eccentrically rotating (orbiting) components of the machining apparatus so that vibrations are eliminated or substantially attenuated during working operations of the apparatus.
For this purpose the inner cylindrical body is configured such that the center of gravity thereof is positioned to match the center of gravity of the spindle unit rotatably supported in the eccentric hole of the inner cylindrical body such that a common center of gravity of the inner cylindrical body and the spindle unit coincides with the center axis of the inner cylindrical body, and wherein the outer cylindrical body is configured such that the center of gravity thereof is positioned to match the common center of gravity of the inner cylindrical body and the spindle unit such that a common center of gravity of the outer cylindrical body and the inner cylindrical body with the spindle unit coincide with the center axis of the outer cylindrical body. Thus, this is made possible owing to the fact that the common center of gravity of the rotating radial offset mechanism and all components rotating together therewith is positioned to coincide, or substantially coincide, with the principal axis, irrespective of the prevailing radial offset of the cutting tool.